The present invention relates to an improved injection molding machine base. One aspect of the present invention relates to an injection molding machine having an improved machine base. An aspect of the invention is an improved injection molding machine base having as an integral part of the base a return conduit for the hydraulic liquid in the system which is connected to receive the hydraulic exhaust from the equipment on the machine and to convey it back to the reservoir.
Hydraulic injection molding machines for molding plastic are old in the art. These are characterized by the use of a hydraulic liquid to clamp the mold parts together and by the use of hydraulic liquid to drive the plasticating device and to inject the plastic into the mold. The hydraulic liquid is circulated at high pressure and in substantial volume. Commercially available clamping tonnages actually go up to about 5000 tons, meaning that the machine holds together the mold parts with a force of 5000 tons and that the injection force of the plastic trying to force open the mold can equal that 5000 tons.
It is common practice in the construction of hydraulic injection molding machines of this kind to provide individual hydraulic circuits for each hydraulic motor on the machine. Commonly, the hydraulic liquid moves from a reservoir to a pump thence through a hydraulic pump discharge manifold or accumulator to a conduit to the particular prime mover (which may be a piston-and-cylinder, a rotary motor of some kind, or a hydraulic control valve), employed in the prime mover or bypassed around it if the control system so requires on that occasion, then passed into a low pressure return line by which it is conveyed to the reservoir. It is also normal practice to direct a large part of the hydraulic liquid through an oil cooler to hold its temperature within an acceptable range. The conduits have ordinarily been a mix of rigid (i.e. steel) hydraulic tubing and flexible hydraulic hose.
The point is, that prior practice for building injection molding machines provided almost every hydraulic unit on the machine with its individual exhaust line extending from its discharge to an oil cooler and back to the reservoir where it is filtered and whence it is recirculated. The large number of hydraulic conduits and fittings required for such systems has increased the risk of hydraulic liquid leaks; further, the back pressure therein has required additional power consumption.
The present invention reduces the number of individual hydraulic return lines and/or the length thereof by directing each hydraulic discharge into a common return line that is formed in the machine base. This common return line, or manifold, is substantially straight, has no internal obstructions, and can be readily opened at its ends for cleaning. Flexible hydraulic hoses are used whenever possible, especially to connect the prime mover exhaust to the machine base. Advantages realized with the present construction compared with a similar machine using prior art hydraulic systems demonstrates the lower hydraulic pressure and velocity is realized with attendent reduction in wear, noise, oil loss and power consumption, heat, and number of components.
Prior art machinery has generally avoided putting oil conduits in the base, possibly because thermal effects warp the base and disturb machine alignment. Several published designs however have included flow passages or reservoirs in machine bases e.g. U.S. Pat. Nos. 1,716,132; 2,568,783 and 3,977,189. The present invention has not encountered any significant problems from this source.
More particularly, the present invention contemplates a machine base for a hydraulic injection molding machine for molding plastic and resin material in a multiple part mold comprising a generally rectangular body to be placed on a horizontal support surface; a plurality of longitudinally spaced apart mounting pads supported from and above said body for supporting machine elements thereon such as a means to plasticate and inject plastic into a mold cavity, a fixed mold platen to receive part of a mold, and a fixed rear platen for supporting hydraulic clamping means; one of the long sides of said rectangular body being a hollow elongated conduit defined by substantially axially straight walls, a removable closure sealably mounted to each end of said conduit, a large (exit) port through a conduit wall near one end of said conduit, and a plurality of (inlet) ports through said conduit wall and smaller than said large port located between said large port and the other end of said conduit, the passsageway of said conduit being substantially the same size throughout the length thereof whereby removal of both closures exposes said conduit its full length to facilitate cleaning.